Neuroimmunological diseases of the central nervous system (CNS) represent a broad spectrum of very diverse diagnoses, most of which are considered rare disorders. With the exception of multiple sclerosis (MS), acute demyelinating encephalomyelitis (ADEM), transverse myelitis (TM) and CNS lupus, reported cohorts in the literature rarely exceed 10-20 patients, and it takes years to collect these numbers. Additionally, with the exception of MS, virtually all reports focus on clinical findings and there is a great paucity of data characterizing intrathecal or systemic immune responses in these patients. As a result, the pathophysiology of these diseases is poorly understood and effective therapies are very rare.[unreadable] Emerging data indicate that the immune response is shaped not only by pathogens, but also by the tissue where the inflammatory process develops. From this standpoint CNS tissue is rather unique. Elegant animal data indicate that foreign grafts survive indefinitely if transplanted into CNS tissue, bypassing systemic presentation of its antigens, whereas they are readily rejected when transplanted into other organs. Indeed, interactions of T cells with neurons can shape T cell effector phenotype, from pathogenic to more regulatory. There is little doubt that these complex immunoregulatory mechanisms emerged as an assurance that CNS tissue, which is vital for the function and survival of the host, will be protected from inadvertent damage by the immune system. Therefore, the apparent failure of the immune system that presents clinically as CNS autoimmunity may originate as a breakdown of natural immunoregulatory mechanisms that govern CNS-immune system interactions.[unreadable] This project studies intrathecal and systemic immune responses in patients referred to Neuroimmunology branch (NIB) for diagnostic work-ups of neuroimmunological CNS disorders. The goal of this study is to define the pathophysiological mechanisms underlying the development of disability in immune-mediated disorders of the CNS and to distinguish these from physiological (and often beneficial) responses of the human immune system to CNS injury. The long-term objective of the study is to acquire knowledge that would allow us to therapeutically inhibit the pathogenic mechanisms and enhance repair mechanisms in immune-mediated CNS diseases, thereby minimizing the extent of CNS tissue damage and promoting recovery. Additionally, we expect that these studies will lead to the development of biomarkers (imaging, immunological and molecular) reflecting concurrent immune-mediated and neurodegenerative pathophysiological mechanisms. This will lead to rational development and faster screening of process-specific therapies, and will permit identification of patients with prevailing disease mechanisms, which is a requirement for individualized medicine approach. Ultimately, understanding the mechanisms of disease processes will impact the management of immune-mediated diseases of the CNS as a whole.